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Full text of "Rapid Population Growth Consequences And Policy Implications"

siblings and performance on six mental tests. For purposes of analysis, he considered "four main factors or underlying types of ability: general, verbal-educational, spatial-mechanical, and physical." His findings, which he compared with those of the Scottish Mental Survey, are shown in Table 10.
TABLE 10
Mean Standard Scores of Recruits on Mental Tests of Different Types, by Number of Siblings, Great Britain, 1946
						Scottish
Number of	Frequency		Verbal-	Spatial-		Mental
Siblings	(Percent)	General	Educational	Mechanical	Physical	Survey
None	13.3	106.6	107.2	104.6	102.3	105.8
1	22.0	105.8	105.8	104.3	101.6	105.1
2	18.6	101.8	101.7	101.7	100.8	101.6
3	13.8	98.8	98.5	99.5	99.8	98.6
4	10.4	94.9	94.7	96.7	98.7	95.8
5	7.8	93.2	92.9	95.2	97.7	94.2
6	5.2	92.4	92.6	93.5	96.4	92.8
7-8	5.5	88.9	91.6	92.9	96.5	91.8
9-11	2.8	87.9	88.2	90.6	96.2	90.1
12-17	0.4	87.2	86.2	91.6	95.8	86.5
Source: Vernon (43).
Equally clear data are available from the United States. In their extensive study of mental retardation in Minnesota covering the period 1910-1960, Reed and Reed (44) reported on the findings of a subsample of 1,016 families in which I.Q.'s were available for both parents and at least one child—a total of 2,032 parents and 2,039 children. They describe this population with care and, among other points, note that:
. , . the sub-sample seemed to be identical with the expectations for an intelligence curve of a normal population in Minnesota. . . . The striking differences to be presented are certainly not due to testing errors. (44, p. 64)
Their findings for this population are shown in Table 11; the figures require no comment. The figures from their study, as well as those from the Scottish survey and the scores from Vernon's "general" test (43), are shown graphically in Figure 8.
Interesting insight is provided by Scott (45), who in 1959 and 1960 studied over 4,000 London school children aged 10 to 11. Boys and girls were represented about equally, and they were "a cross-section of children attend-in? nrdinarv dav schools in London." Heights and weights. ;is wp.ll ;is tnfnrnvu pp. 34-35) Source:  Douglas (35).he negative correlation between intelligence and family size varied among the classes. It was "clearly apparent" in children of fanners, manual laborers, and clerical workers, "negligible" in children from the managerial class, and "barely discernible" among those from the professional class.